Deadliest mass shootings in modern US history

At least 59 people were killed and more than 515 others were wounded when a gunman opened fire on a country music festival in Las Vegas, Nevada, on Sunday night.

The gunman, Stephen Paddock, 64, acted alone, taking aim at the crowd of 22,000 concertgoers from his room on the 32nd floor of the Mandalay Bay Casino across the street.

It is the worst mass shooting the United States has ever seen in modern history, and Paddock's motive remains unclear. This week's massacre is among a series of such incidents that have plagued America in recent years.

Below are the deadliest shootings in the U.S. since 1900, starting with the most recent attack:

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The deadliest mass shootings in the US since 1900

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The deadliest mass shootings in the US since 1900

On October 1, 2017 in Las Vegas, Nevada, gunman Stephen Paddock opened fire on concertgoers below from the windows of his suite at the Mandalay Bay Resort and Casino.

As of October 3, at least 59 people are dead and over 500 injured in what became the deadliest mass shooting in United States history.

(Photo by David Becker/Getty Images)

Five Dallas police officers were shot and killed by Micah Xavier Johnson, 25, as they guarded a group of protesters on July 7, 2016.

(Photo via REUTERS/Carlo Allegri)

On June 12, 2016, Omar Mateen opened fire inside Pulse Nightclub, a well-known LGBT club in Orlando, Florida, killing 49 people and injuring 58.

REUTERS/Carlo Allegri/File Photo

Chris Harper-Mercer, 26, opened fire on the Umpqua Community College campus in Roseburg, Oregon, killing nine people and wounding nine others before he was shot dead by police on October 1, 2015.

(Photo by Scott Olson/Getty Images)

White supremacist Dylann Roof, 21, opened fire at Emanuel African Methodist Episcopal Church in Charleston, South Carolina, during a bible study, leaving nine churchgoers dead on June 18, 2015.

(REUTERS/Brian Snyder)

Rival motorcycle gangs killed nine at a restaurant in Waco, Texas, on May 18, 2015. More than 190 people are arrested.

(REUTERS/Waco Police Department/Handout)

Fourteen people were killed and 22 were wounded when married couple Syed Rizwan Farook and Tashfeen Malik attacked a service center for people with developmental disabilities during its holiday party in San Bernadino, California, on Dec. 2, 2015.

(Photo by Barbara Davidson/The Los Angeles Times via Getty Images)

A college student killed six people, three in his apartment and others on the streets of Isla Vista, California, on May 23, 2014. The mentally ill gunman committed suicide.

(Photo by Irfan Khan/Los Angeles Times via Getty Images)

A former Navy reservist working as a government contractor killed 12 people at the Washington Navy Yard on Sept. 16, 2013. He was shot dead by police.

(Photo by Mark Wilson/Getty Images)

On December 14, 2012, Adam Lanza attacked Sandy Hook Elementary School in Newtown, Connecticut, killing 20 children and six school staff members.

(Photo by James Keivom/NY Daily News via Getty Images)

A masked gunman killed 12 people and wounded 70 when he opened fire on July 20, 2012, at a midnight premiere of the Batman film "The Dark Knight Rises" in Aurora, Denver.

(REUTERS/Evan Semon)

A white supremacist opened fire in the Sikh Temple of Wisconsin in Oak Creek, Wisconsin, on August 6, 2012, killing six people.

(REUTERS/John Gress)

Then-U.S. Rep. Gabrielle Giffords (D-AZ) was the target of an assassination attempt by a gunman in Tucson, Arizona, on Jan. 8, 2011. More than a dozen other people were injured and six people were killed at a public event entitled 'Congress on Your Corner' when a gunman opened fire.

(Photo by James Palka/Getty Images)

U.S. Army Major Nidal Malik Hasan, an army psychiatrist, killed 13 people and wounded 30 in a shooting at Fort Hood military base on November 5, 2009.

(Photo by Joe Raedle/Getty Images)

On April 3, 2009, 41-year-old Jiverly Antares Wong killed 13 people inside an immigration center in Binghamton, New York.

(Photo by Spencer Platt/Getty Images)

On April 16, 2007, gunman Seung-Hui Cho killed 32 people on the campus of Virginia Tech in Blacksburg, Virginia.

A gunman killed five girls in a one-room Amish schoolhouse October 2, 2006, in Nickel Mines, Pennsylvania. The man entered the school, let the boys go free, tied up the girls and shot them execution-style before killing himself.

(Photo by William Thomas Cain/Getty Images)

Two men, John Allen Muhammad, 41, and Lee Boyd Malvo, 17, ambushed 13 people, killing 10 of them, in sniper-style shootings that terrorized the Washington D.C. area for three weeks in October 2002. Muhammad was executed and Malvo was sentenced to life in prison.

(Photo credit should read LUKE FRAZZA/AFP/Getty Images)

The Columbine High School massacre was perpetrated by students Eric Harris and Dylan Klebold who killed 12 fellow students and one teacher on April 20, 1999.

(Photo via REUTERS/Gary Caskey GCC/HB)

George Hennard killed 23 people and injured 27 others when he attacked Luby's Cafeteria in Killeen, Texas, on October 16, 1991.

(Photo by Gaylon Wampler/The LIFE Images Collection/Getty Images)

James Huberty, pictured here, shot and killed 21 people and hurt 19 others at a McDonald's restaurant in San Ysidro, California, on July 18, 1984.

(Photo via Getty Images)

Student Charles Whitman climbed to the top of the clock tower at the University of Texas where he shot and killed 13 people after killing his mother and wife on August 1, 1966.

(Photo via Getty Images)

The Ludlow massacre took place when members of the Colorado National Guard as well as other militiamen shot down 19 striking coal miners in 1914.